pf2e.fyi
From Pathfinder Lost Omens The Grand Bazaar, which isn't enabled.

Lingering Flames

FEAT 8
ARCHETYPE
Archetype Spell Trickster
Prerequisites Spell Trickster Dedication; ability to cast fireball

When you cast Fireball, you can modify its effects, decreasing the base damage to 5d6 and causing it to deal 2 persistent fire damage to creatures that fail their save, doubled as normal on a critical failure. If you do, replace its heightened entry with the following.

Heightened (+1) The damage is increased by 1d6 and the persistent fire damage is increased by 2.
Pathfinder Lost Omens The Grand BazaarOGL